1. Field of the Invention
The present invention relates to a toner for use in an image forming method such as an electrophotographic process for visualizing an electrostatic charge image, or in a toner jet method.
2. Description of the Related Art
Various image forming methods, such as an electrostatic recording method, a magnetic recording method and a toner jet method, have been known.
Recently, in a copying apparatus, miniaturization, weight saving, high process speed and reliability are increasingly sought. Such a copying apparatus is now being utilized not only for the so-called office copier for copying an original, but also as a digital printer for a computer output, for copying a high definition image such as graphic designs, and for light printing (print on demand applications capable of producing various kinds of small volume printed matter, ranging from document editing by the aid of a personal computer to copying and book binding). For this reason, a fixing ability for various types of paper has been required.
As a resin for a toner, a polyester resin and a vinyl-type copolymer such as a styrene-type resin have been primarily utilized. Polyester resin is basically excellent in its low-temperature fixing ability, but is also disadvantageous in that an offset phenomenon is liable to occur at high temperature. In order to rectify such a drawback, if the viscosity of the polyester resin is raised by increasing the molecular weight thereof, not only the low-temperature fixing ability but also crushability in toner production is lowered, thereby becoming unsuitable for forming finer toner particles.
The vinyl-type copolymer such as styrene-type resin is excellent in crushability in toner production and in high-temperature offset resistance because a higher molecular weight can be easily obtained. However, in order to improve the low-temperature fixing property, if the molecular weight is reduced, the blocking resistance and the developing property are lowered.
In order to effectively exploit the advantages of these two resins and to cover the drawbacks thereof, a toner is disclosed using at least two of a polyester resin, a styrene-type resin, and a resin formed by reacting parts of a polyester resin and a styrene-type resin (see, for example, Japanese Patent Application Laid-open Nos. H11-194536 and 2000-056511).
These technologies can improve the compatibility between the polyester resin and the vinyl-type copolymer and provide a toner having a wide fixing temperature range, which however is still insufficient to accomplish the same fixing property for various types of paper, ranging from thick paper having surface irregularities to very thin paper, as recently required for light printing.
A technology is disclosed in which the low-temperature fixing property is improved by controlling frequency dependence of a synthesized curve obtained by frequency dispersion measurement of the viscoelasticity of the toner (see, for example, Japanese Patent Application Laid-open No. H04-199061). In addition, a technology is disclosed providing a wide fixing range by controlling the elastic modulus of toner (see, for example, Japanese Patent Application Laid-open No. H08-234480).
However, these technologies still have room for improvement, in consideration of dealing with high-speed image formation in light printing, and various types of paper. Also in the case where printed matter itself is dealt with as merchandise, there is room for improvement as a change in image quality results from deterioration in toner.